Cheng Jin-Tao, Li Xiang, Yao Feng-Zhen, Shan Nan, Li Ya-Hui, Zhang Zhen-Xian, Sui Xiao-Lei
Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, College of Agronomy and Biotechnology, China Agricultural University, Beijing 100193, China,; Huazhong Agricultural University, Wuhan 430070, China.
Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, College of Agronomy and Biotechnology, China Agricultural University, Beijing 100193, China,.
Plant Sci. 2015 Aug;237:46-56. doi: 10.1016/j.plantsci.2015.05.006. Epub 2015 May 18.
Many hexose transporters (HTs) have been reported to play roles in sucrose-transporting plants. However, little information about roles of HTs in RFOs (raffinose family oligosaccharides)-transporting plants has been reported. Here, three hexose transporters (CsHT2, CsHT3, and CsHT4) were cloned from Cucumis sativus L. Heterologous expression in yeast demonstrated that CsHT3 transported glucose, galactose and mannose, with a K(m) of 131.9 μM for glucose, and CsHT4 only transported galactose, while CsHT2 was non-functional. Both CsHT3 and CsHT4 were targeted to the plasma membrane of cucumber protoplasts. Spatio-temporal expression indicated that transcript level of CsHT3 was much higher than that of CsHT2 and CsHT4 in most tissues, especially in peduncles and fruit tissues containing vascular bundles. GUS staining of CsHT3-promoter-β-glucuronidase (GUS) transgenic Arabidopsis plants revealed CsHT3 expression in tissues with high metabolic turnover, suggesting that CsHT3 is involved in sugar competition among different sink organs during plant development. The transcript levels of CsHT3 and cell wall invertase genes increased in peduncles and fruit tissues along with cucumber fruit enlargement, and CsHT3 localized to phloem tissues by immunohistochemical localization; These results suggest that CsHT3 probably plays an important role in apoplastic phloem unloading of cucumber fruit.
据报道，许多己糖转运蛋白（HTs）在运输蔗糖的植物中发挥作用。然而，关于HTs在运输棉子糖家族寡糖（RFOs）的植物中的作用，报道的信息很少。在此，从黄瓜中克隆了三个己糖转运蛋白（CsHT2、CsHT3和CsHT4）。在酵母中的异源表达表明，CsHT3转运葡萄糖、半乳糖和甘露糖，对葡萄糖的Km为131.9μM，而CsHT4只转运半乳糖，而CsHT2无功能。CsHT3和CsHT4都定位于黄瓜原生质体的质膜。时空表达表明，在大多数组织中，尤其是在含有维管束的果梗和果实组织中，CsHT3的转录水平远高于CsHT2和CsHT4。CsHT3启动子-β-葡萄糖醛酸酶（GUS）转基因拟南芥植株的GUS染色显示，CsHT3在代谢周转高的组织中表达，这表明CsHT3在植物发育过程中参与不同库器官之间的糖竞争。随着黄瓜果实的膨大，果梗和果实组织中CsHT3和细胞壁转化酶基因的转录水平升高，通过免疫组织化学定位发现CsHT3定位于韧皮部组织；这些结果表明，CsHT3可能在黄瓜果实的质外体韧皮部卸载中起重要作用。
